1. Field of the Invention
The present invention concerns a thrust reverser having internal clamshells which is designed to be mounted on aircraft engines of the turbojet-engine bypass or straight flow types.
2. Description of the Related Art
Usually thrust reversers mounted downstream of the engine assume a dual function: to form an exhaust nozzle in the forward-thrust mode; and to implement thrust reversal in the thrust-reversal mode.
In fact, these thrust reversers, called "target" or "clamshell" reversers, are fitted with two clamshells pivoting on a stationary or fixed structure, usually affixed to a cowling surrounding the turbo-jet engine.
These thrust reversers offer the advantage of being comparatively simple and lightweight. The kinematics is simple. The clamshells form the engine exhaust nozzle in the forward-thrust mode and form baffles causing flow reversal in the thrust-reversal mode.
As regards this type of downstream-baffles thrust reverser, designs using a stationary pivot means are known, for example, from French patent 2,348,371 and U.S. Pat. No. 3,550,855, wherein the pivot means are mounted downstream of the leading edge of the thrust reverser doors to assure sufficient distance from said doors relative to the engine exhaust in the thrust-reversal mode.
U.S. Pat. No. 2,847,823 discloses a thrust reverser fitted with downstream baffles and comprising a stationary, rear ring. FIG. 1 of the attached drawings shows an embodiment of this known type of thrust-reverser.
In this instance, the thrust reverser consists of a stationary upstream structure 1 affixed to the turbojet engine 2, or its cowling, an inner wall 3 externally bounding an annular duct 4, through which fluid flow passes, and an external fairing 5 affixed to the inner wall 3 and two side structures 6. Two downstream baffles, i.e. clamshells 7a and 7b, are pivotably mounted on the stationary structure 1, in particular using pivots 8 supported in the side structures 6. The side structure 6 also support a system controlling the displacement and locking of the clamshells 7a and 7b.
A downstream end 9 of the clamshells 7a and 7b, constituting the trailing edge of the outer wall extended beyond the downstream side of the fairing 5, is not coplanar. Thus, during forward-thrust operation when the clamshells 7a and 7b are integrated into the duct's outer wall in the extension of stationary structure 1, large aerodynamic losses may severely degrade the desired performance. This is because the clamshells 7a and 7b must remain slanted relative to the reversed flow and leaks between the two clamshells must be minimized to achieve the required thrust-reversal.
Corrective solutions already have been suggested. Illustratively, the French patent document A 2,638,783 proposes adding movable side flaps to the thrust reverser. This, however, requires hinge means and entails the drawbacks of increased complexity, less reliability, and increased weight, contrary to ever-desired weight reduction for aeronautical applications.
Similarly, the French patent document A 2,601,077 calls for a stationary structure downstream of the thrust-reverser baffles. Consequently, the lengthening of the duct and the means required to displace the baffles and achieve a sufficient opening in the thrust-reversal position upstream of said stationary structure entail increased weight as well.
Moreover, pivoting inner-clamshell thrust reversers are known. U.S. Pat. No. 4,790,495 illustrates one embodiment which has the drawback of a remnant, unsmooth outer rear cowling profile resulting in aerodynamic losses and requiring a complex control-and-locking system. Another design solution, described in U.S. Pat. No. 4,340,178, proposes a system of clamshell pivots on rails. The system raises complexity-and-reliability problems and involves increased weight.